**Core Concept**
Pituitary diabetes insipidus is a condition characterized by the inadequate production of antidiuretic hormone (ADH), also known as vasopressin, leading to excessive thirst and polyuria. This deficiency results from either a lack of ADH secretion by the posterior pituitary gland or the inability of the kidneys to respond to ADH.

**Why the Correct Answer is Right**
Desmopressin, a synthetic analogue of ADH, is the primary treatment for uncomplicated pituitary diabetes insipidus. It works by mimicking the action of natural ADH, promoting water reabsorption in the kidneys and thereby reducing urine output and thirst. Desmopressin is available in oral and nasal spray forms, offering flexibility in treatment administration.

**Why Each Wrong Option is Incorrect**
**Option A:** Vasopressin is a natural hormone that, while effective, has a shorter duration of action and may cause more side effects compared to desmopressin.
**Option B:** Thiazide diuretics can be used in some cases of nephrogenic diabetes insipidus but are not the primary treatment for pituitary diabetes insipidus.
**Option C:** Hydrochlorothiazide is a type of thiazide diuretic and is not suitable for the treatment of pituitary diabetes insipidus.

**Clinical Pearl / High-Yield Fact**
Desmopressin is a long-acting analogue of ADH, offering a convenient and effective treatment option for patients with uncomplicated pituitary diabetes insipidus.

**Correct Answer: D. Desmopressin**